U.S. patent number 9,239,496 [Application Number 13/861,231] was granted by the patent office on 2016-01-19 for display with column spacer structures for enhanced light leakage and pooling resistance.
This patent grant is currently assigned to Apple Inc.. The grantee listed for this patent is Apple Inc.. Invention is credited to Cheng Chen, Enkhamgalan Dorjgotov, Zhibing Ge, Jun Qi.
United States Patent |
9,239,496 |
Ge , et al. |
January 19, 2016 |
Display with column spacer structures for enhanced light leakage
and pooling resistance
Abstract
A display may have a layer of liquid crystal material between a
color filter layer and a thin-film transistor layer. Column spacer
structures may be formed between the color filter layer and the
thin-film transistor layer to maintain a desired separation between
the color filter and thin-film transistor layers. The column spacer
structures may be formed from polymer structures such as
photoresist pillars and may include metal pads. The metal pads may
be formed on the upper surface of the thin-film transistor layer or
the lower surface of the color filter layer. The photoresist
pillars may be formed on a surface in the display such as the lower
surface of the color filter layer. Column spacer structures may
include main spacer structures, subspacer structures, and
intermediate thickness spacer structures to enhance pooling mura
and light leakage performance.
Inventors: |
Ge; Zhibing (Sunnyvale, CA),
Chen; Cheng (San Jose, CA), Dorjgotov; Enkhamgalan (San
Francisco, CA), Qi; Jun (Cupertino, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
|
|
Assignee: |
Apple Inc. (Cupertino,
CA)
|
Family
ID: |
50687671 |
Appl.
No.: |
13/861,231 |
Filed: |
April 11, 2013 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20140307207 A1 |
Oct 16, 2014 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F
1/13394 (20130101); G02F 1/13398 (20210101); G02F
1/13396 (20210101) |
Current International
Class: |
G02F
1/1339 (20060101) |
Field of
Search: |
;349/155,157 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Lee et al., U.S. Appl. No. 13/741,138, filed Jan. 14, 2013. cited
by applicant.
|
Primary Examiner: Briggs; Nathanael R
Attorney, Agent or Firm: Treyz Law Group, P.C. Treyz; G.
Victor Guihan; Joseph F.
Claims
What is claimed is:
1. A display, comprising: a color filter layer; a thin-film
transistor layer; a layer of liquid crystal material between the
color filter layer and the thin-film transistor layer; and a
plurality of column spacer structures between the color filter
layer and the thin-film transistor layer, wherein the column spacer
structures include first column spacer structures of a first
thickness, second column spacer structures of a second thickness,
and third column spacers of a third thickness that is between the
first and second thicknesses, and wherein a density of the third
column spacers in the display is less than a density of the second
column spacers in the display.
2. The display defined in claim 1 wherein the column spacer
structures include fourth column spacer structures of a fourth
thickness that is between the first and third thicknesses.
3. The display defined in claim 2 wherein at least some of the
column spacer structures include photoresist pillars and metal
pads.
4. A display, comprising: a first display layer; a second display
layer; and a layer of liquid material between the first and second
display layers, wherein the first and second display layers are
separated by a distance; and spacer structures between the first
and second display layers that include first spacer structures of a
first thickness, second spacer structures of a second thickness,
and third spacers of a third thickness that is between the first
and second thicknesses, wherein the first thickness is equal to the
distance, and wherein the second spacer structures cover a greater
area of the display than the third spacers.
5. The display defined in claim 4 wherein the spacer structures
include polymer structures and metal pads.
6. The display defined in claim 5 wherein the polymer structures
comprise first polymer structures in the first spacer structures,
second polymer structures in the second spacer structures, and
third polymer structures in the third spacer structures and wherein
the first, second, and third polymer structures have equal
thicknesses.
7. A display, comprising: a color filter layer having a lower
surface; a thin-film transistor layer having an upper surface; a
liquid crystal layer between the lower surface and the upper
surface; and a plurality of column spacers between the color filter
layer and the thin-film transistor layer, wherein first and second
column spacers of the plurality of column spacers have respective
first and second metal pads, and wherein the first and second metal
pads have different thicknesses.
8. The display defined in claim 7 wherein the plurality of column
spacers comprises a main column spacer, a subspacer column spacer,
and an intermediate column spacer, wherein the first metal pad is
associated with the main column spacer and has a first thickness,
and wherein the second metal pad is associated with the
intermediate column spacer and has a second thickness that is less
than the first thickness.
9. The display defined in claim 8 wherein no metal pads are
positioned beneath the subspacer column spacer.
10. The display defined in claim 9 wherein the first and second
metal pads are located on the upper surface of the thin-film
transistor layer.
11. The display defined in claim 9 wherein the first or second
metal pad is located on the lower surface of the color filter
layer.
12. The display defined in claim 9 wherein the plurality of column
spacers comprises an additional intermediate column spacer that has
a third metal pad with a third thickness, wherein the third
thickness is less than the first thickness, and wherein the third
thickness is different than the second thickness.
13. The display defined in claim 12 wherein the main column spacer
is formed on the lower surface of the color filter layer.
14. The display defined in claim 12 wherein the subspacer column
spacer is formed on the lower surface of the color filter
layer.
15. The display defined in claim 14 wherein the intermediate column
spacer is formed on the lower surface of the color filter
layer.
16. The display defined in claim 14 wherein the second metal pad is
formed on the lower surface of the color filter layer, and wherein
the intermediate column spacer is formed on the second metal
pad.
17. The display defined in claim 14 wherein the main column spacer,
intermediate column spacer, and the subspacer column spacer all
have the same thickness.
18. The display defined in claim 7 wherein the plurality of column
spacers comprises main column spacers, subspacer column spacers,
and intermediate column spacers, wherein the main column spacers
are associated with main metal pads that have a first thickness,
and wherein the intermediate column spacers are associated with
intermediate metal pads that have a second thickness that is less
than the first thickness.
19. The display defined in claim 18 wherein the density of the
intermediate metal pads is less than the density of the main metal
pads.
Description
BACKGROUND
This relates generally to electronic devices, and more
particularly, to electronic devices with displays.
Electronic devices often include displays. For example, cellular
telephones and portable computers often include displays for
presenting information to a user.
Liquid crystal displays contain a layer of liquid crystal material.
Display pixels in a liquid crystal display contain thin-film
transistors and electrodes for applying electric fields to the
liquid crystal material. The strength of the electric field in a
display pixel controls the polarization state of the liquid crystal
material and thereby adjusts the brightness of the display
pixel.
Substrate layers such as color filter layers and thin-film
transistor layers are used in liquid crystal displays. The
thin-film transistor layer contains an array of the thin-film
transistors that are used in controlling electric fields in the
liquid crystal layer. The color filter layer contains an array of
color filter elements such as red, blue, and green elements. The
color filter layer provides the display with the ability to display
color images.
In an assembled display, the layer of liquid crystal material is
sandwiched between the thin-film transistor layer and the color
filter layer. Polyimide passivation layers cover the inner surface
of the color filter layer and the upper surface of the thin-film
transistor layer. An array of column spacers is formed on the inner
surface of the color filter layer to maintain a desired gap between
the color filter layer and the thin-film transistor layer. Column
spacers are typically formed from hard organic materials such as
photoresist.
There are typically two types of column spacers in a liquid crystal
display. A relatively sparse set of main column spacers extends
between the color filter layer and the thin-film transistor layer.
The thickness of the column spacers and their associated landing
pads establishes the amount of separation between the color filter
layer and the thin-film transistor layer. Another set of column
spacers, referred to as subspacers, has structures that extend only
partway between the color filter layer and the thin-film transistor
layer. Subspacers are used to prevent the thin-film transistor
layer and column spacer from contacting one another. The subspacers
do not extend all the way between the color filter layer and
thin-film transistor layer to accommodate deformation of the color
filter layer relative to the thin-film transistor upon a drop in
ambient temperature for the display.
There are tradeoffs involved when determining an appropriate number
column spacers to use in a given display. If too few of the main
column spacers are provided, there will be insufficient support for
the display. This will make the display susceptible to an
undesirable visual effect called pooling mura. If too many of the
main column spacers are provided, the display will become overly
stiff. This will make the display prone to stress-induced
birefringence when deformed, leading to undesired light leakage
effects. With existing column spacer designs, it can be challenging
to identify an acceptable tradeoff between pooling and light
leakage. Displays are often sensitive to manufacturing variations
and may exhibit more pooling and light leakage effects than
desired.
It would therefore be desirable to be able to provide a display
with an improved column spacer configuration.
SUMMARY
A display may have a color filter layer with opposing upper and
lower surfaces and a thin-film transistor layer with opposing upper
and lower surfaces. A layer of liquid crystal material may be
located between the lower surface of the color filter layer and the
upper surface of the thin-film transistor layer.
Column spacer structures may be formed between the color filter
layer and the thin-film transistor layer to maintain a desired
separation between the color filter layer and the thin-film
transistor layer. The column spacer structures may be formed from
polymer structures such as photoresist pillars and may include pads
such as metal pads. The metal pads may be formed on the upper
surface of the thin-film transistor layer or the lower surface of
the color filter layer. The photoresist pillars may be formed on a
surface in the display such as the lower surface of the color
filter layer.
Column spacer structures may include main spacer structures,
subspacer structures, and one or more different types of
intermediate thickness spacer structures. The use of the
intermediate thickness spacer structures may simultaneously improve
pooling mura performance and light leakage performance.
Further features of the invention, its nature and various
advantages will be more apparent from the accompanying drawings and
the following detailed description of the preferred
embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an illustrative electronic device
such as a laptop computer with a display in accordance with an
embodiment of the present invention.
FIG. 2 is a perspective view of an illustrative electronic device
such as a handheld electronic device with a display in accordance
with an embodiment of the present invention.
FIG. 3 is a perspective view of an illustrative electronic device
such as a tablet computer with a display in accordance with an
embodiment of the present invention.
FIG. 4 is a perspective view of an illustrative electronic device
such as a computer display with display structures in accordance
with an embodiment of the present invention.
FIG. 5 is a cross-sectional side view of an illustrative display in
accordance with an embodiment of the present invention.
FIG. 6 is a cross-sectional side view of a portion of a display
with a main column spacer that is supported by a landing pad on a
thin-film transistor layer in accordance with an embodiment of the
present invention.
FIG. 7 is a cross-sectional side view of a portion of a display
with a main column spacer that is supported by a pad on a color
filter layer in accordance with an embodiment of the present
invention.
FIG. 8 is a cross-sectional side view of a portion of a display
with a main column spacer that extends between a pad on a color
filter layer and a pad on a thin-film transistor layer in
accordance with an embodiment of the present invention.
FIG. 9 is a cross-sectional side view of a portion of a display
with a column spacer formed on a color filter layer and separated
from a thin-film transistor layer by a gap in accordance with an
embodiment of the present invention.
FIG. 10 is a cross-sectional side view of a portion of an
illustrative display having column spacer structures of different
thicknesses in accordance with an embodiment of the present
invention.
FIG. 11 is a graph in which pooling and light leakage performance
values have been plotted as a function of main column spacer
density in accordance with an embodiment of the present
invention.
FIG. 12 is a table of illustrative column spacer characteristics
that may be used in a column spacer arrangement in accordance with
an embodiment of the present invention.
FIG. 13 is a cross-sectional side view of a portion of a display
having main column spacer structures, subspacer structures, and
intermediate column spacer structures using pads of different
thicknesses on the surface of a thin-film transistor layer in
accordance with an embodiment of the present invention.
FIG. 14 is a cross-sectional side view of a portion of a display
having main column spacer structures, subspacer structures, and
intermediate column spacer structures using pads of different
thicknesses on the surface of a thin-film transistor layer and on
the surface of a color filter layer in accordance with an
embodiment of the present invention.
FIG. 15 is a cross-sectional side view of a portion of a display
having main column spacer structures, subspacer structures, and two
different types of intermediate column spacer structures with
respective first and second intermediate column spacer thicknesses
in accordance with an embodiment of the present invention.
DETAILED DESCRIPTION
Electronic devices may include displays. The displays may be used
to display images to a user. Illustrative electronic devices that
may be provided with displays are shown in FIGS. 1, 2, 3, and
4.
FIG. 1 shows how electronic device 10 may have the shape of a
laptop computer having upper housing 12A and lower housing 12B with
components such as keyboard 16 and touchpad 18. Device 10 may have
hinge structures 20 that allow upper housing 12A to rotate in
directions 22 about rotational axis 24 relative to lower housing
12B. Display 14 may be mounted in upper housing 12A. Upper housing
12A, which may sometimes referred to as a display housing or lid,
may be placed in a closed position by rotating upper housing 12A
towards lower housing 12B about rotational axis 24.
FIG. 2 shows how electronic device 10 may be a handheld device such
as a cellular telephone, music player, gaming device, navigation
unit, or other compact device. In this type of configuration for
device 10, housing 12 may have opposing front and rear surfaces.
Display 14 may be mounted on a front face of housing 12. Display 14
may, if desired, have openings for components such as button 26.
Openings may also be formed in display 14 to accommodate a speaker
port (see, e.g., speaker port 28 of FIG. 2).
FIG. 3 shows how electronic device 10 may be a tablet computer. In
electronic device 10 of FIG. 3, housing 12 may have opposing planar
front and rear surfaces. Display 14 may be mounted on the front
surface of housing 12. As shown in FIG. 3, display 14 may have an
opening to accommodate button 26 (as an example).
FIG. 4 shows how electronic device 10 may be a computer display or
a computer that has been integrated into a computer display. With
this type of arrangement, housing 12 for device 10 may be mounted
on a support structure such as stand 27. Display 14 may be mounted
on a front face of housing 12.
The illustrative configurations for device 10 that are shown in
FIGS. 1, 2, 3, and 4 are merely illustrative. In general,
electronic device 10 may be a laptop computer, a computer monitor
containing an embedded computer, a tablet computer, a cellular
telephone, a media player, or other handheld or portable electronic
device, a smaller device such as a wrist-watch device, a pendant
device, a headphone or earpiece device, or other wearable or
miniature device, a television, a computer display that does not
contain an embedded computer, a gaming device, a navigation device,
an embedded system such as a system in which electronic equipment
with a display is mounted in a kiosk or automobile, equipment that
implements the functionality of two or more of these devices, or
other electronic equipment.
Housing 12 of device 10, which is sometimes referred to as a case,
may be formed of materials such as plastic, glass, ceramics,
carbon-fiber composites and other fiber-based composites, metal
(e.g., machined aluminum, stainless steel, or other metals), other
materials, or a combination of these materials. Device 10 may be
formed using a unibody construction in which most or all of housing
12 is formed from a single structural element (e.g., a piece of
machined metal or a piece of molded plastic) or may be formed from
multiple housing structures (e.g., outer housing structures that
have been mounted to internal frame elements or other internal
housing structures).
Display 14 may be a touch sensitive display that includes a touch
sensor or may be insensitive to touch. Touch sensors for display 14
may be formed from an array of capacitive touch sensor electrodes,
a resistive touch array, touch sensor structures based on acoustic
touch, optical touch, or force-based touch technologies, or other
suitable touch sensor components.
Display 14 for device 10 includes display pixels formed from liquid
crystal display (LCD) components or other suitable image pixel
structures.
A display cover layer may cover the surface of display 14 or a
display layer such as a color filter layer or other portion of a
display may be used as the outermost (or nearly outermost) layer in
display 14. The outermost display layer may be formed from a
transparent glass sheet, a clear plastic layer, or other
transparent member.
A cross-sectional side view of an illustrative configuration for
display 14 of device 10 (e.g., for display 14 of the devices of
FIG. 1, FIG. 2, FIG. 3, FIG. 4 or other suitable electronic
devices) is shown in FIG. 5. As shown in FIG. 5, display 14 may
include backlight structures such as backlight unit 42 for
producing backlight 44. During operation, backlight 44 travels
outwards (vertically upwards in dimension Z in the orientation of
FIG. 5) and passes through display pixel structures in display
layers 46. This illuminates any images that are being produced by
the display pixels for viewing by a user. For example, backlight 44
may illuminate images on display layers 46 that are being viewed by
viewer 48 in direction 50.
Display layers 46 may be mounted in chassis structures such as a
plastic chassis structure and/or a metal chassis structure to form
a display module for mounting in housing 12 or display layers 46
may be mounted directly in housing 12 (e.g., by stacking display
layers 46 into a recessed portion in housing 12). Display layers 46
may form a liquid crystal display or may be used in forming
displays of other types.
In a configuration in which display layers 46 are used in forming a
liquid crystal display, display layers 46 may include a liquid
crystal layer such a liquid crystal layer 52. Liquid crystal layer
52 may be sandwiched between display layers such as display layers
58 and 56. Layers 56 and 58 may be interposed between lower
polarizer layer 60 and upper polarizer layer 54.
Layers 58 and 56 may be formed from transparent substrate layers
such as clear layers of glass or plastic. Layers 56 and 58 may be
layers such as a thin-film transistor layer and/or a color filter
layer. Conductive traces, color filter elements, transistors, and
other circuits and structures may be formed on the substrates of
layers 58 and 56 (e.g., to form a thin-film transistor layer and/or
a color filter layer). Touch sensor electrodes may also be
incorporated into layers such as layers 58 and 56 and/or touch
sensor electrodes may be formed on other substrates.
With one illustrative configuration, layer 58 may be a thin-film
transistor layer that includes an array of thin-film transistors
and associated electrodes (display pixel electrodes) for applying
electric fields to liquid crystal layer 52 and thereby displaying
images on display 14. Layer 56 may be a color filter layer that
includes an array of color filter elements for providing display 14
with the ability to display color images. If desired, layer 58 may
be a color filter layer and layer 56 may be a thin-film transistor
layer.
During operation of display 14 in device 10, control circuitry
(e.g., one or more integrated circuits on a printed circuit) may be
used to generate information to be displayed on display 14 (e.g.,
display data). The information to be displayed may be conveyed to a
display driver integrated circuit such as circuit 62A or 62B using
a signal path such as a signal path formed from conductive metal
traces in a rigid or flexible printed circuit such as printed
circuit 64 (as an example).
Backlight structures 42 may include a light guide plate such as
light guide plate 78. Light guide plate 78 may be formed from a
transparent material such as clear glass or plastic. During
operation of backlight structures 42, a light source such as light
source 72 may generate light 74. Light source 72 may be, for
example, an array of light-emitting diodes.
Light 74 from light source 72 may be coupled into edge surface 76
of light guide plate 78 and may be distributed in dimensions X and
Y throughout light guide plate 78 due to the principal of total
internal reflection. Light guide plate 78 may include
light-scattering features such as pits or bumps. The
light-scattering features may be located on an upper surface and/or
on an opposing lower surface of light guide plate 78.
Light 74 that scatters upwards in direction Z from light guide
plate 78 may serve as backlight 44 for display 14. Light 74 that
scatters downwards may be reflected back in the upwards direction
by reflector 80. Reflector 80 may be formed from a reflective
material such as a layer of white plastic or other shiny
materials.
To enhance backlight performance for backlight structures 42,
backlight structures 42 may include optical films 70. Optical films
70 may include diffuser layers for helping to homogenize backlight
44 and thereby reduce hotspots, compensation films for enhancing
off-axis viewing, and brightness enhancement films (also sometimes
referred to as turning films) for collimating backlight 44. Optical
films 70 may overlap the other structures in backlight unit 42 such
as light guide plate 78 and reflector 80. For example, if light
guide plate 78 has a rectangular footprint in the X-Y plane of FIG.
5, optical films 70 and reflector 80 may have a matching
rectangular footprint.
To maintain a desired gap for the liquid crystal material between
the lower surface of color filter layer 56 and the upper surface of
thin-film transistor layer 58, display 14 may be provided with
column spacer structures (sometimes referred to as post spacers).
The column spacer structures may be formed from column structures
(e.g., cylindrical posts) and/or planar structures such as metal
pads on the surfaces of color filter layer 56 and/or thin-film
transistor layer 58.
FIGS. 6, 7, 8, and 9 are cross-sectional side views of a portion of
display 14 in arrangements with different respective column spacer
structures (sometimes referred to as column spacers). The
arrangements of FIG. 6, 7, 8, or 9, other column spacer structures,
and combinations of two or more of these configurations may be used
in forming column spacer structures for display 14. In the example
of FIG. 6, column spacer structures 100 extend between lower
(innermost) surface 114 of color filter layer 56 and upper
(outermost) surface 116 of thin-film transistor layer 58.
Column spacer structures 100 of FIG. 6 include column spacer 102
and landing pad 104. Column spacer structures such as column spacer
102 and other column spacers in display 14 may be formed from
photoresist, other polymers, or non-polymer materials.
Photolithographic fabrication techniques may be used to pattern
column spacers on layers such as color filter layer 56. Landing pad
104 may be formed from an organic or inorganic material. As an
example, landing pad 104 may be formed from metal. Both the
thickness (vertical height in dimension Z) of landing pad 104 on
surface 116 of thin-film transistor layer 58 and the thickness of
column spacer 102 contribute to the total thickness of column
spacer structures 100. If desired, column spacer 102 may extend
only to position 108 so that a gap such as gap 110 may be formed
between the lower surface of column spacer 102 of column spacer
structures 100 and upper surface 106 of pad 104.
If desired, column spacer structures 100 may be formed in display
14 using a configuration in which a pad (e.g., metal pad 104) is
formed on lower surface 114 of color filter layer 56, as shown in
FIG. 7. Column spacer 102 may be formed on top of pad 104. The
total thickness of column spacer structures 100 in this scenario is
made up of the thickness of pad 104 plus the thickness of column
spacer 102. As with the illustrative configuration of FIG. 6,
column spacer structures 100 of FIG. 7 may extend from lower
surface 114 of color filter 56 to upper surface 116 of thin-film
transistor layer 58 or may extend from surface 114 to position 108
so that a gap such as gap 110 is formed between the lower surface
of column spacer structures 100 and upper surface 116 of thin-film
transistor layer.
In the illustrative arrangement of FIG. 8, pads such as metal pads
have been formed above and below column spacer 102. In particular,
metal pad 104-1 has been formed on surface 114 of color filter
layer 56 and metal pad 104-2 has been formed on surface 116 of
thin-film transistor layer 58. In this type of configuration,
column spacer structures 100 may include a column spacer such as
column spacer 102 that extends between metal pads 104-1 and 104-2
or a column spacer that extends from pad 104-1 to surface 108 to
create gap 110 between the column spacer and the upper surface of
pad 104-2.
As shown in FIG. 9, column spacer structures 100 may include a
column spacer such as column spacer 102 that is formed directly on
surface 114 of color filter layer 56. Mating landing pads need not
be provided on surface 116 of thin-film transistor layer 58. Gap
110 may separate the lower surface of column spacer 102 from upper
surface 116 of thin-film transistor layer 58.
FIG. 10 is a cross-sectional side view of a portion of display 14
in a configuration in which there are three different types of
column spacer structures between color filter layer 56 and
thin-film transistor layer 58. As shown in FIG. 10, color filter
layer 56 may include substrate 120 and color filter element array
122. Substrate 120 may be formed from a transparent planar member
such as a clear layer of glass or plastic. Color filter array 122
may be formed on the lower surface of substrate 120. Color filter
array 122 may contain an array of color filter elements 124
separated by a grid of opaque masking lines such as masking lines
126. Color filter elements 124 may be formed from colored polymers
(e.g., red, blue, and green photoresist elements). Covering layers
128 may be clear material (e.g., polymer material). Thin-film
transistor layer 58 may be formed from a layer of thin-film
transistor circuitry 125 (e.g., transistors formed from thin film
layers, electrodes, patterned signal lines, capacitors, and other
display pixel array circuitry). Thin-film transistor circuitry 125
may be formed on thin-film transistor substrate 127. Substrate 127
may be a layer of clear glass, plastic, or other material. Coatings
(e.g., polymer coating layers) may be formed on the surfaces of
color filter layer 56 and thin-film transistor layer 58 (e.g.,
coatings that cover pad structures on these surfaces).
Column spacer structures 100A, 100B, and 100C may be formed by
depositing column spacers on surface 114 of color filter layer 56
such as column spacers 102A, 102B, and 102C. One or more masks
(e.g., binary masks, halftone masks, and/or grayscale masks) may be
used in forming photoresist pillars (column spacers) of different
thicknesses. Landing pads such as landing pad 104 and other pad
structures may overlap column spacers such as column spacer 102A
and may be used to prevent scratches in the surfaces of the display
layers and/or to make desired thickness adjustments in the column
spacer structures. Metal or other materials may be used in forming
pads.
In display 14, there are generally numerous column spacer
structures such as column spacer structures 100A, numerous column
spacer structures such as column spacer structures 100B, and
numerous column spacer structures such as column spacer structures
100C and structures 100A, 100B, and 100C are generally distributed
uniformly across the surface of display 14. The portion of display
14 shown in FIG. 10 in which there is a single one of each of these
types of column spacer structures is merely illustrative.
Column spacers 102A, 102B, and 102C have different thicknesses
(sometimes referred to as heights). For example, column spacer 102A
of FIG. 10 may have a thickness (height) H1, column spacer 102B of
FIG. 10 may have a thickness (height) H2, and column spacer 102C of
FIG. 10 may have a thickness (height) H3. The values of H1, H2, and
H3 may all be different (as an example).
Column spacer structures 100A (and column spacers 102A) may
sometimes be referred to as main column spacer structures (or main
column spacers). As shown in FIG. 10, main column spacer structures
100A extend between lower surface 114 of color filter layer 56 and
upper surface 116 of thin-film transistor layer 58, so that there
is no gap in the column spacer structures. The main column spacer
structures 100A therefore define the separation distance between
color filter layer 56 and thin-film transistor layer 58 in which
liquid crystal material 52 is placed.
Column spacer structures 100B do not extend all the way between
surface 114 on color filter layer 56 and surface 116 on thin-film
transistor layer 58 and are therefore sometimes referred to as
subspacers. As shown in FIG. 10, column subspacer structures 100B
are free of metal pads such pad 104. There is a gap .DELTA.H
between subspacer column spacer 102B and upper surface 116 of
thin-film transistor layer 58. In conditions in which the
temperature of liquid crystal material 52 (FIG. 5) changes, color
filter layer 56 may deform towards thin-film transistor layer 58.
Color filter layer 56 may also be deformed toward thin-film
transistor layer 58 when pressure is applied to color filter layer
56. In situations such as these, gap .DELTA.H temporarily
disappears because the lower surface of column spacer 102B comes
into contact with surface 116 of thin-film transistor layer. The
presence of column spacer structures 100B is therefore used to
arrest motion of color filter layer 56 to prevent color filter
layer 56 and thin-film transistor layer 58 from contacting one
another during use of display 14.
Column spacer structures 100C form a gap .DELTA.H' that is
intermediate in size between the size of gap .DELTA.H associated
with subspacer column spacer structures 100B and the zero gap size
associated with main column spacer structures 100A. The thickness
of column spacer structures 100C also lies between the thickness of
main column spacer structures 100A and the thickness of subspacer
column spacer structures 100B. Column spacer structures 100C may
therefore sometimes be referred to as intermediate column spacer
structures, intermediate thickness column spacer structures, or
transitional column spacer structures.
Intermediate column spacer structures 100C are thicker than
subspacer structures 100B (e.g., intermediate column spacers 102
are thicker than subspacer column spacers 102B) and therefore
provide more support for the layers of display 14 than subspacer
column spacers 100B. This can help display 14 resist undesired
pooling mura. As shown in FIG. 10, intermediate column spacer
structures 100C may have intermediate thickness column spacers 102C
of thickness H3 that are separated from surface 116 of thin-film
transistor layer 158 by gap .DELTA.H' (which is different than
.DELTA.H).
There are generally tradeoffs to be considered between light
leakage performance and pooling performance in a display such as
display 14 of FIG. 10. FIG. 11 is a graph in which pooling
performance has been plotted on the left-hand vertical axis as a
function of main column spacer concentration and in which light
leakage performance has been plotted on the right-hand vertical
axis as a function of main column spacer concentration.
Pooling mura curve 140 illustrates how pooling performance tends to
degrade as the concentration of main column spacers in a display
decreases. This is because the column spacer structures in a
display help to prevent layers 56 and 58 from coming into contact
with each other. By providing a sufficient number of main column
spacers, pooling performance can be improved, as indicated by the
downward slope of curve 140 in of FIG. 11.
Light leakage curve 142 illustrates how stress-induced
birefringence and therefore light leakage tends to become worse as
the number of main column spacers in a display increases. For a
given deformation in the planarity of display 14, stress tends to
rise in proportion to the stiffness of the display. Displays with
fewer main column spacers are more flexible than displays with more
column spacers. As a result, displays with fewer main column
spacers develop less stress when deformed and produce
correspondingly less stress-induced birefringence and light leakage
(undesired localized brightening of the display). This behavior is
reflected by the upwards slope of curve 142. When fewer main column
spacers are present (near the left-hand side of curve 142 in FIG.
11), light leakage performance is better. When more main column
spacers are present (near the right-hand side of curve 142 in FIG.
11), light leakage performance is worse.
The inclusion of intermediate thickness column spacer structures
such as column spacer structures 100C that have thicknesses greater
than that of subspacer structures 100B enhances pooling mura
performance by providing additional structural support for the
layers of display 14 during temperature changes and other forces
that exert bending pressure on layers such as color filter layer 56
without causing excessive stiffness of the type that may result by
increasing the number of main column spacers 102A in display 14.
The benefit of including intermediate thickness column spacer
structures such as column spacer structures 100C of FIG. 10 into
display 14 is illustrated by dashed curve 144.
As illustrated by arrows 146, curve 144 represents an improvement
over curve 140 resulting from the inclusion of intermediate column
spacers. When trading off light leakage performance against pooling
mura performance in a display without intermediate column spacer
structures 100C, a display might be configured to use the number of
main column spacers associated with point 148 of the graph of FIG.
11. When trading off light leakage performance against pooling mura
performance in a display with intermediate column spacer structures
100C, in contrast, a display might be configured to use the number
of main column spacers associated with point 150 of the graph of
FIG. 11. When display 14 is configured in accordance with point
150, both pooling mura performance and light leakage performance
can be improved relative to a display configured in accordance with
point 148.
FIG. 12 is a table showing illustrative numbers (in percentages) of
main column spacer density, intermediate column spacer density, and
subspacer column spacer density that may be used in display 14. The
table of FIG. 12 also shows illustrative thicknesses for column
spacers 102A, 102B, and 102C and shows illustrative gap sizes
.DELTA. (zero for the main column spacers, non-zero for the
intermediate column spacers and subspacers).
If desired, column spacer structures can use upper and/or lower
pads (e.g., metal pads) and/or column spacers of different
thicknesses to achieve desired overall thicknesses for the column
spacer structures. Consider, as an example, the arrangement of FIG.
13. In this configuration, main column spacer structures 100A are
formed from main column spacers 102A on surface 114 of color filter
layer 56 and landing pad 104 on surface 116 of thin-film transistor
layer 58. Subspacer column spacer structures 100B are formed from
subspacer 102B on surface 114 of color filter layer 56.
Intermediate column spacer structures 100C of FIG. 13 are formed
from intermediate column spacer 102C and pad 104C on surface 116 of
thin-film transistor layer 58. The thickness of spacers 102A, 102B,
and 102C may, if desired, all be equal (H1).
In the example of FIG. 13, two types of pads are being used--pads
such as pad 104A serve as part of the main column spacer structures
for display 14 and pads such as pad 104C serve as part of the
intermediate column spacer structures for display 14. Other
combinations of pads may be used in the column spacer structures if
desired (see, e.g., FIGS. 6, 7, 8, and 10). The example of FIG. 14
in which two different thicknesses of pads on surface 116 of
thin-film transistor layer are used in two different types of
column spacer structures is merely illustrative.
FIG. 14 is a cross-sectional side view of a portion of display 14
in a configuration in which the thickness H1 of each column spacer
is the same and in which pad 104C has been formed on surface 114 of
color filter layer 56. In general, pads may be formed on surface
114, on surface 116, or on a combination of surfaces 114 and 116.
If desired, subspacer column spacer structures 100B (and/or
structures 100A and/or structures 100C) may include one or more
pads, as described in connection with FIGS. 6, 7, and 8.
The example of FIG. 15 involves the use of four different types of
column spacer structure. In addition to main column spacer
structures 100A and subspacer column spacer structures 100B, the
column spacer structures of FIG. 15 include first and second
intermediate column spacer structures 100C-1 and 100C-2, each with
a different respective thickness. In the FIG. 15 example, main
column spacer structures 100A are formed from main column spacer
102A and main column spacer pad 104A and subspacer column spacer
structures 100B are formed from subspacer column spacer 102B
(without a pad). Intermediate column spacer structures 100C-1 have
been formed without using a pad by using intermediate column spacer
102C-1 of thickness H3. Intermediate column spacer structures
100C-2 are formed from a column spacer 102C-2 of thickness H2,
which is the same as the thickness of subspacer column spacer 102B
and which is different from main column spacer thickness H1 of main
column spacer 102A. Pad 104C-2 and spacer 102C-2 contribute to the
overall thickness of column spacer structures 100C-2. To provide
two different levels of intermediate column support for display 14,
the thickness of intermediate column spacer structures 100C-1 is
preferably different than the thickness of intermediate column
spacer structures 100C-2.
The foregoing is merely illustrative of the principles of this
invention and various modifications can be made by those skilled in
the art without departing from the scope and spirit of the
invention.
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